Dual Cathode Ion Source

ABSTRACT

An ion source having dual indirectly heated cathodes is disclosed. Each of the cathodes may be independently biased relative to its respective filament so as to vary the profile of the beam current that is extracted from the ion source. In certain embodiments, the ion source is used in conjunction with an ion implanter. The ion implanter comprises a beam profiler to measure the current of the ribbon ion beam as a function of beam position. A controller uses this information to independently control the bias voltages of the two indirectly heated cathodes so as to vary the uniformity of the ribbon ion beam. In certain embodiments, the current passing through each filament may also be independently controlled by the controller.

This application is a continuation of U.S. patent application Ser. No.15/416,131 filed Jan. 26, 2017, the disclosure of which is incorporatedherein by reference in its entirety.

FIELD

Embodiments relate to an apparatus and method for tuning a ribbon ionbeam extracted from an ion source, and more particularly, toindependently tuning the power levels to each cathode in a dual cathodeion source.

BACKGROUND

Ions are used in a plurality of semiconductor processes, such asimplantation, amorphization, deposition and etching processes. Theseions may be created within an ion source chamber and extracted throughan extraction aperture in the ion source chamber.

In certain embodiments, the ion source comprises an indirectly heatedcathode. A filament is disposed behind the cathode and energized to emitthermionic electrons. These electrons then strike the back surface ofthe cathode, causing the cathode to increase in temperature and emitelectrons into the ion source chamber. These energized electrons collidewith a feed gas in the ion source chamber to create ions, which can beextracted through an extraction aperture in the ion source.

In some embodiments, the extraction aperture is in the shape of anelongated slit, having a length that is much greater than its height.The ions are extracted through this extraction aperture in the form of aribbon ion beam. One parameter that is monitored in ion implanters ision beam uniformity. This term refers to the consistency of beam currentacross the entire length of the ribbon ion beam. Components that arelocated downstream from the ion source may be utilized to compensate forany non-uniformity in the ribbon ion beam extracted from the ion source.However, these components tend to reduce the overall beam current andmay cause the ion beam to lose some amount of parallelism.

Thus, it would be beneficial if there were an apparatus that allowedimproved control over the ion beam that is extracted from the ionsource. Further, it would be advantageous if there were a method tocontrol that apparatus which allowed the ribbon ion beam to be tunedwithout sacrificing beam current and parallelism.

SUMMARY

An ion source having dual indirectly heated cathodes is disclosed. Eachof the cathodes may be independently biased relative to its respectivefilament so as to vary the profile of the beam current that is extractedfrom the ion source. In certain embodiments, the ion source is used inconjunction with an ion implanter. The ion implanter comprises a beamprofiler to measure the current of the ribbon ion beam as a function ofbeam position. A controller uses this information to independentlycontrol the bias voltages of the two indirectly heated cathodes so as tovary the uniformity of the ribbon ion beam. In certain embodiments, thecurrent passing through each filament may also be independentlycontrolled by the controller. Further, in certain embodiments, eachcathode is independently biased relative to the ion source.

According to one embodiment, an ion source is disclosed. The ion sourcecomprises a first end wall and a second end wall; chamber wallsconnected to the first end wall and the second end wall to define an ionsource chamber, wherein one of the chamber walls comprises an extractionaperture, wherein a ribbon ion beam is extracted through the extractionaperture; a first cathode disposed proximate the first end wall; a firstfilament disposed between the first end wall and the first cathode; afirst bias power supply to bias the first cathode relative to the firstfilament; a second cathode disposed proximate the second end wall; asecond filament disposed between the second end wall and the secondcathode; and a second bias power supply, different from the first biaspower supply, to bias the second cathode relative to the secondfilament. In certain embodiments, an output of the first bias powersupply is different from an output of the second bias power supply, soas to change a uniformity of the ribbon ion beam extracted through theextraction aperture.

In some embodiments, the ion source is part of an ion implanter. The ionimplanter comprises the ion source, a beam profiler for measuring a beamcurrent of the ribbon ion beam as a function of beam position; and acontroller in communication with the ion source and the beam profiler,such that the controller controls an output of the first bias powersupply and the second bias power supply so as to vary a uniformity ofbeam current of the ribbon ion beam. In certain embodiments, the ionimplanter further comprises a corrector magnet, wherein the controllercontrols the corrector magnet to improve uniformity of the ribbon ionbeam after adjusting the output of the first bias power supply and thesecond bias power supply. In some embodiments, the controller determinesthe uniformity of the ribbon ion beam based on input from the beamprofiler and adjusts the output of the first bias power supply and thesecond bias power supply so as to improve the uniformity of the beamcurrent. In certain embodiments, the ion source further comprises afirst arc power supply to bias the first cathode relative to walls ofthe ion source and a second arc power supply to bias the second cathoderelative to the walls of the ion source, wherein the controller controlsan output of the first arc power supply and the second arc power supplyso as to vary uniformity of the beam current of the ribbon ion beam.

According to another embodiment, an ion implanter is disclosed. The ionimplanter comprises an ion source, comprising a first end wall and asecond end wall; chamber walls connected to the first end wall and thesecond end wall to define an ion source chamber, wherein one of thechamber walls comprises an extraction aperture through which a ribbonion beam is extracted; a first cathode disposed proximate the first endwall; a first filament disposed between the first end wall and the firstcathode; a first bias power supply to bias the first cathode relative tothe first filament; a first arc power supply to bias the first cathoderelative to the chamber walls; a second cathode disposed proximate thesecond end wall; a second filament disposed between the second end walland the second cathode; a second bias power supply, different from thefirst bias power supply, to bias the second cathode relative to thesecond filament; and a second arc power supply to bias the secondcathode relative to the chamber walls; a beam profiler for measuring abeam current of the ribbon ion beam as a function of beam position; anda controller in communication with the ion source and the beam profiler,such that the controller adjusts at least one of a plurality of theparameters of the ion source so as to vary uniformity of beam current ofthe ribbon ion beam, wherein the parameters are selected from the groupconsisting of filament currents, bias voltages supplied by the firstbias power supply and the second bias power supply, and arc voltagessupplied by the first arc power supply and the second arc power supply.In certain embodiments, the controller controls at least two parameters.In certain embodiments, the controller determines the uniformity of theribbon ion beam based on input from the beam profiler and adjusts the atleast one of the parameters so as to improve the uniformity of the beamcurrent.

According to another embodiment, a method of adjusting a uniformity of aribbon ion beam extracted from a dual cathode ion source is disclosed.The method comprises measuring a current of the ribbon ion beam acrossits length at a plane of a workpiece; and adjusting a parameter of thedual cathode ion source to adjust the uniformity of the ribbon ion beamin response to a measured current, wherein the parameter of the dualcathode ion source is selected from the group consisting of a currentflowing through a first filament, a current flowing through a secondfilament, a voltage between the first filament and a first cathode; avoltage between the second filament and a second cathode; a voltagebetween the first cathode and a wall of the dual cathode ion source anda voltage between the second cathode and the wall of the dual cathodeion source. In certain embodiments, the uniformity is adjusted by makingthe voltage between the first filament and the first cathode differentfrom the voltage between the second filament and the second cathode. Incertain embodiments, the uniformity is adjusted by making the voltagebetween the first cathode and the wall of the dual cathode ion sourcedifferent from the voltage between the second cathode and the wall ofthe dual cathode ion source.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding of the present disclosure, reference is madeto the accompanying drawings, which are incorporated herein by referenceand in which:

FIG. 1 shows a dual cathode ion source for controlling the uniformity ofthe ribbon ion beam as it is extracted from the ion source according toone embodiment;

FIG. 2 shows an ion implanter system that utilizes the dual cathode ionsource of FIG. 1;

FIGS. 3A-3C show the effect that changing the bias voltages may have onthe ribbon ion beam;

FIG. 4 shows a sequence to tune a ribbon ion beam using the ionimplanter of FIG. 2; and

FIGS. 5A-5C show how the ribbon ion beam may be tuned according to oneembodiment.

DETAILED DESCRIPTION

FIG. 1 shows a first embodiment of a dual cathode ion source 100 thatmay be used to control uniformity of a ribbon ion beam 1 as it isextracted from the ion source. In this embodiment, the ion source 100comprises a plurality of chamber walls 111 and two end walls 113,defining an ion source chamber 110.

The dual cathode ion source 100 may have one dimension that is longerthan the other two dimensions. This dimension may be referred to as thelength of the ion source. The four chamber walls 111 extend in thelength dimension. The other two chamber walls may be referred to as endwalls 113 a, 113 b. The one of the four chamber walls 111 that extendsin the length dimension includes an extraction aperture 115. The chamberwall 111 that includes the extraction aperture 115 may be referred to asthe faceplate. The extraction aperture 115 may be configured such thatits length is much greater than its height. In certain embodiments, thelength of the extraction aperture 115 may be more than 100 mm, althoughother dimensions are also possible. The height of the extractionaperture 115 may be much smaller, such as about 5 mm or less.

Disposed on each end wall 113 a, 113 b is an indirectly heated cathode.A first filament 120 a extends into the ion source chamber 110,proximate end wall 113 a. This first filament 120 a is electricallyconductive and is in communication with a first filament power supply125 a. The first filament power supply 125 a is used to supply a currentthat passes through the first filament 120 a. A first cathode 130 a isdisposed in the ion source chamber 110 such that the first filament 120a is disposed between the first cathode 130 a. This arrangement limitsthe exposure of the first filament 120 a to the gasses, plasma and ionsthat are disposed in the ion source chamber 110. The first cathode 130 ais also made of an electrically conductive material, such as titanium,graphite, molybdenum or tungsten. A first bias power supply 135 a isused to bias the first cathode 130 a relative to the first filament 120a. For example, the first cathode 130 a may be biased positivelyrelative to the first filament 120 a so as to attract the thermionicelectrons emitted by the first filament 120 a toward the first cathode130 a. The first cathode 130 a may be biased relative to the firstfilament 120 a by using the bias power supply 135 a to output a voltage.Alternatively, the first bias power supply 135 a may be configured tosupply a current to create the bias between the first filament 120 a andthe first cathode 130 a. The combination of the first filament 120 a andthe first cathode 130 a form a first indirectly heated cathode.

The second end wall 113 b also includes a second filament 120 b, asecond filament power supply 125 b, a second cathode 130 b and a secondbias power supply 135 b. These components operate in the same manner asdescribed above. Thus, the second filament 120 b and the second cathode130 b form a second indirectly heated cathode.

When two filament power supplies 125 a, 125 b are used, the currentsupplied to each filament 120 a, 120 b may be different. In certainembodiments, a single filament power supply is used to supply current toboth filaments 120 a, 120 b.

The bias power supplies 135 a, 135 b may be independently controlledsuch that the output by each bias power supply 135 a, 135 b may bedifferent. The ability to independently control the bias voltage to eachcathode 130 a, 130 b is beneficial in the ability to tune the ribbon ionbeam 1.

The ion source 100 also includes two arc power supplies 140 a, 140 bwhich are used to bias the cathodes 130 a, 130 b, respectively, relativeto the chamber walls 111. By utilizing two arc power supplies 140 a, 140b, it is possible to separately bias each cathode 130 a, 130 b relativeto the chamber walls 111. The chamber walls 111 may be biased positivelyrelative to the cathodes 130 a, 130 b so that electrons emitted from thecathodes 130 a, 130 b can be accelerated equivalent to the bias voltage,collide with neutral species and generate ions. In certain embodiments,there may be one arc power supply such that both cathodes 130 a, 130 bis commonly biased relative to the chamber walls 111.

Located outside the ion source chamber 110 and proximate the extractionaperture 115 are one or more electrodes. In one embodiment, there is asuppression electrode 160 disposed proximate the extraction aperture115. The suppression electrode 160 has a suppression aperture throughwhich the ribbon ion beam 1 passes. There may also be a ground electrode170 disposed proximate the suppression electrode 160. The groundelectrode 170 has a ground aperture through which the ribbon ion beam 1passes. The suppression electrode 160 and the ground electrode 170 areboth made from an electrically conductive material. The suppressionelectrode 160 may be negatively biased relative to the chamber walls111, such as by a suppression power supply, so as to extract and focusthe positive ions through the extraction aperture 115. The groundelectrode 170 may be grounded.

In operation, a feed gas, stored in a gas container 180, is introducedinto the ion source chamber 110 via a gas inlet 181. Power is suppliedfrom the filament power supplies 125 a, 125 b to the filaments 120 a,120 b, which causes current to pass through these filaments 120 a, 120b. As the filaments 120 a, 120 b heat, thermionic electrons are emitted.These electrons are attracted toward the respective cathode 130 a, 130 bsince the cathodes 130 a, 130 b are positively biased relative to thefilaments 120 a, 120 b. The bombardment of electrons into the backsurface of the cathodes 130 a, 130 b cause the cathodes 130 a, 130 b tobecome hot enough to emit electrons from the front surface into the ionsource chamber 110.

The electrons emitted from the cathodes 130 a, 130 b collide with thefeed gas to create ions in the ion source chamber 110. These ions arethen extracted from the ion source chamber 110 through the extractionaperture 115 in the form of a ribbon ion beam 1. The ribbon ion beam 1then passes through the suppression aperture in the suppressionelectrode 160 and the ground aperture in the ground electrode 170, andcontinues through the ion implanter.

FIG. 2 shows a representative ion implanter 250 that utilizes the ionsource 100. After the ribbon ion beam 1 passes through the suppressionelectrode 160 and the ground electrode 170, the ribbon ion beam 1 entersa mass analyzer 200. The mass analyzer 200, having a resolving aperture201, is used to remove unwanted components from the ribbon ion beam 1,resulting in a ribbon ion beam 1 having the desired energy and masscharacteristics passing through resolving aperture 201. Ions of thedesired species then pass through a first deceleration stage 210, whichmay include one or more electrodes. The output of the first decelerationstage 210 may be a diverging ion beam.

A corrector magnet 220 is adapted to deflect the divergent ion beam intoa set of individual beamlets having substantially parallel trajectories.The corrector magnet 220 may comprise a magnetic coil and magnetic polepieces that are spaced apart to form a gap, through which the ionbeamlets pass. The magnetic coil is energized so as to create a magneticfield within the gap, which deflects the ion beamlets in accordance withthe strength and direction of the applied magnetic field. The magneticfield is adjusted by varying the current through the magnetic coil.Alternatively, other structures, such as parallelizing lenses, can alsobe utilized to perform this function.

In certain embodiments, the corrector magnet 220 may also comprise othercomponents that are used to improve the uniformity of the ribbon ionbeam 1. For example, quadrature pole magnets, rods and energy puritymodules may be employed to manipulate the ribbon ion beam 1, attemptingto improve its uniformity. These components manipulate the ribbon ionbeam 1 so as to make the beam current nearly uniform across its entirelength, while maintaining the parallelism of the individual ionbeamlets.

Following the corrector magnet 220, the ribbon ion beam 1 is targetedtoward the workpiece. In some embodiments, a second deceleration stage230 may be added between the workpiece and the second deceleration stage230.

A beam profiler 240 may also be disposed downstream from the seconddeceleration stage 230. In one embodiment, the beam profiler 240 maycomprise a plurality of charge or current collectors, known as dose cups241, which are arranged along the length of the ribbon ion beam. Inother embodiments, the dose cups 241 are scanned across the ion beam tomeasure beam characteristics such as beam current, uniformity and beamangles. In this way, it is possible to analyze the beam current as afunction of beam position. This information may be used to tune theribbon ion beam, as will be described in more detail below.

The beam profiler 240 is disposed at the position where the workpiece isnormally disposed. In other words, the beam profiler 240 measures theribbon ion beam 1 at the same position where it impacts the workpiece.After the beam profiler 240 has finished scanning, it is moved to astowed position so that the workpiece may be disposed in the path of theribbon ion beam 1.

Further, a controller 245 may be disposed in the ion implanter 250. Thecontroller 245 may include a processing unit and a storage element. Thestorage element may be any suitable non-transitory memory device, suchas semiconductor memory (i.e. RAM, ROM, EEPROM, FLASH RAM, DRAM, etc.),magnetic memory (i.e. disk drives), or optical memory (i.e. CD ROMs).The storage element may be used to contain the instructions, which whenexecuted by the processing unit in the controller 245, allow the ribbonion beam 1 to be tuned, as described in more detail below.

The controller 245 may be in communication with the beam profiler 240.The controller 245 may also be in communication with the first biaspower supply 135 a, the second bias power supply 135 b, the firstfilament power supply 125 a, the second filament power supply 125 b, thefirst arc power supply 140 a, the second arc power supply 140 b and thecorrector magnet 220.

Unexpectedly, the dual cathode ion source 100 may also be used to adjustthe uniformity of the ribbon ion beam 1. For example, in one experiment,a ribbon ion beam made up of arsenic ions was created at an energy of 30keV. The beam current, uniformity and beam angles, as a function of beamposition of the ribbon ion beam, were measured by the beam profiler 240.FIGS. 3A-3C show the beam profile, measured in mA/cm, at the plane ofthe workpiece. In these figures, a beam position of 0 mm is defined asthe middle of the ribbon ion beam 1, negative values of beam positionare to the left of the middle of the ribbon ion beam 1 and positivevalues of beam position are to the right of the middle of the ribbon ionbeam. The vertical axis is representative of the beam current density atthat position. In FIG. 3A, the first bias power supply 135 a and thesecond bias power supply 135 b are set to the same output (i.e. the samebias voltage or same bias current). As seen in FIG. 3A, the left side ofthe ribbon ion beam 1 has somewhat higher beam current than the rightside. Further, the ribbon ion beam has fairly good uniformity from about−50 mm to 25 mm. Outside this range, the uniformity of the ribbon ionbeam degrades. FIG. 3B shows how this non-uniformity can be exacerbatedby increasing the magnitude of the bias voltage (or current) supplied bythe first bias power supply 135 a as compared to the magnitude of theoutput of the second bias power supply 135 b. In fact, the beam currenton the left side is actually twice the beam current on certain positionson the right side. Further, the beam current decreases almost linearlyas a function of beam position from about −50 mm and about 75 mm.However, as shown in FIG. 3C, by increasing the bias voltage (orcurrent) supplied by the second bias power supply 135 b as compared tothe first bias power supply 135 a, the resulting ribbon ion beam is muchmore uniform. In fact, the ribbon ion beam is roughly uniform from about−60 mm to about 60 mm. Thus, the ribbon ion beam of FIG. 3A may beimproved by independently modifying the outputs of the bias powersupplies 135 a, 135 b. In some embodiments, the uniformity may beimproved when the output of the first bias power supply 135 a differsfrom the output of the second bias power supply 135 b.

Similar trends were also found when experimenting with ribbon ion beamsmade up of phosphorus ions. These effects were created by varying theoutputs of the bias power supplies 135 a, 135 b by between about 1% and5%. Of course, the outputs of the bias power supplies may be varieddifferently, depending on the implementation.

The ability to affect the beam current of the ribbon ion beam using thefirst bias power supply 135 a and the second bias power supply 135 ballows a new method of tuning the ribbon ion beam 1. Additionally, thebeam current may be affected by varying the outputs of the first arcpower supply 140 a and second arc power supply 140 b. Additionally, thebeam current may also be affecting by varying the outputs of the firstfilament power supply 125 a and the second filament power supply 125 b.

In one embodiment, the ion implanter 250 of FIG. 2 may be used to tunethe ribbon ion beam 1 to improve its uniformity. FIG. 4 shows a sequencethat may be used to achieve improved uniformity.

First, as shown in Process 300, the parameters of the ion source 100 isinitially configured. This initial configuration includes setting thearc voltages, the bias voltages and the filament currents of the ionsource 100. In certain embodiments, the filament currents for thefilaments 120 a, 120 b are set to the same initial levels. Similarly, incertain embodiments, the bias voltages for the two cathodes 130 a, 130 bare set to the same initial voltage. Additionally, in certainembodiments, the arc voltages for the two cathodes 130 a, 130 b are setto the same initial voltage.

After the parameters for the ion source 100 are configured, the voltagefor the suppression electrode 160 is established, as shown in Process310. This voltage helps determine the extracted shape (focus and angle)of the ribbon ion beam 1.

The extraction voltage, which determines the final ion beam energy, thedeceleration voltage, which determines the beam transport energy throughthe beamline and the magnetic fields for the mass analyzer 200 andcorrector magnet 220 are also configured, as shown in Process 320. Notethat Process 310 and Process 320 may be performed in the opposite order,if desired.

Once the ion source 100, the suppression electrode 160, the massanalyzer 200 and the corrector magnet 220 are configured, a ribbon ionbeam 1 can be generated. This ribbon ion beam 1 passes through the ionimplanter 250 and strikes the beam profiler 240, so that the beamcurrent can be measured as a function of beam position. For example, thebeam profiler 240 may determine that the ribbon ion beam has the currentprofile shown in FIG. 5A.

The graph in FIG. 5A shows the beam current as a function of beamposition. The interval 501 denotes the part of the ribbon ion beam 1that will impact the workpiece. This interval 501 may also be referredto as the region of interest. In certain embodiments, this region ofinterest may be 300 mm, although other dimensions are also possible. Ascan be seen, the left side of the ribbon ion beam 1 has greater beamcurrent density than the right side of the ribbon ion beam 1. In fact,there is a near linear decrease in the beam current density from theleft end of interval 501 to the right end of interval 501.

This information may be passed to the controller 245. The controller245, based on the beam profile received from the beam profiler 240, maydetermine a change to be applied to the parameters of the ion source100. As described above, the parameters of the ion source 100 includethe bias voltage applied to each cathode 130 a, 130 b, the currentapplied to each filament 120 a, 120 b, and the arc voltage appliedbetween each cathode 130 a, 130 b and the chamber walls 111.

For example, the controller 245 may apply a change in the bias voltagesupplied to one or both of the cathodes 130 a, 130 b. For example, thecontroller 245 may increase the magnitude of the voltage supplied bysecond bias power supply 135 b, decrease the magnitude of the voltagesupplied by first bias power supply 135 a, or a combination of these twoactions. Alternatively, or additionally, the controller 245 may adjustthe current passing through one or both of the filaments 120 a, 120 b byvarying the outputs of filament power supplies 125 a, 125 b. Further, incertain embodiments where two arc power supplies are used, thecontroller 245 may control the arc voltages so that each cathode 130 a,130 b is independently biased relative to the chamber walls 111. Thechanges to the parameters of the ion source 100 are shown in Process340.

After modifying the parameters in the ion source 100, the change in theribbon ion beam 1 is then monitored by the beam profiler 240. Forexample, after adjusting the filament currents, bias voltages, the arcvoltages or a combination of these, the profile of the ribbon ion beam 1may become as shown in FIG. 5B.

The dotted line 502 reflects the original beam current profile beforeProcess 340. The solid line 503 reflects the beam current profile afterProcess 340. After the parameters of the ion source 100 have beenadjusted, any final tuning of the ribbon ion beam 1 may be performed bymodifying the components in the corrector magnet 220, as shown inProcess 350. In certain embodiments, the adjustment of the parameters ofthe ion source 100 occurs before the tuning of the corrector magnet 220.

FIG. 5C shows the resulting ribbon ion beam 1 after completion of thesequence shown in FIG. 4. The solid line 505 reflects the resulting beamprofile after the entire sequence shown in FIG. 4 is performed. Forcomparison, the dotted line 504 shows the resulting beam current profileif the parameters of the ion source 100 are not varied in Process 340.Note that by varying the parameters of the ion source 100, the resultingbeam current is increased. Further, the overall shape of the beamprofile is improved in this embodiment, as the beam current is moreuniform through the interval 501. Furthermore, since less tuning isperformed by the corrector magnet 220, the parallelism of the individualion beamlets may be improved. Further, one of the benefits is that thebeam tuning time/sequence can be shortened.

Thus, in one embodiment, an ion implanter 250 is disclosed, where theion implanter 250 includes the ion source 100 of FIG. 1 and a controller245. Based on measurements of the ribbon ion beam from the beam profiler240, the controller 245 manipulates the parameters of the ion source 100to tune the ribbon ion beam 1. These parameters may include varying thebias voltage supplied to each cathode 130 a, 130 b so that these biasvoltages are not equal. Note that this is possible due to the presenceof a first bias power supply 135 a and a second bias power supply 135 b.In other embodiments, the controller may vary the current passingthrough each filament 120 a, 120 b so that these currents are not equal.Note that this is possible due to the presence of a first filament powersupply 125 a and a second filament power supply 125 b. Finally, incertain embodiments, the arc voltages can be varied such that theoutputs of arc power supply 140 a, 140 b are not equal. Again, this ispossible due to the presence of a first arc power supply 140 a, and asecond arc power supply 140 b.

The present apparatus has many advantages. First, in currentimplementations, the adjustments to the corrector magnet 220 are used tocompensate for non-uniform beam current. These adjustments typicallyreduce the overall beam current and also introduce some degree ofnon-parallelism between individual ion beamlets. The tuning ofparameters of the ion source 100, such as the bias voltage applied toeach cathode 130 a, 130 b, reduces the amount of non-uniformity.Consequently, less compensation is performed by the corrector magnet220, and the beam current is greater and the parallelism is improved.Furthermore, because more control can be exercised over the uniformityof the ion beam by varying the parameters of the ion source 100, thetime to perform the other tuning processes, such as adjusting thecomponents of the corrector magnet 220, can be reduced.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Furthermore, although the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize that its usefulness is not limited thereto andthat the present disclosure may be beneficially implemented in anynumber of environments for any number of purposes. Accordingly, theclaims set forth below should be construed in view of the full breadthand spirit of the present disclosure as described herein.

What is claimed is:
 1. An ion source, comprising: a first end wall and asecond end wall; chamber walls connected to the first end wall and thesecond end wall to define an ion source chamber, wherein one of thechamber walls comprises an extraction aperture, wherein a ribbon ionbeam is extracted through the extraction aperture; a first cathodedisposed proximate the first end wall; a first filament disposed betweenthe first end wall and the first cathode; a first bias power supply tobias the first cathode relative to the first filament; a first filamentpower supply to supply a first current to the first filament; a secondcathode disposed proximate the second end wall; a second filamentdisposed between the second end wall and the second cathode; a secondbias power supply, different from the first bias power supply, to biasthe second cathode relative to the second filament; and a secondfilament power supply to supply a second current to the second filament.2. The ion source of claim 1, wherein an output of the first bias powersupply is different from an output of the second bias power supply, soas to change a uniformity of the ribbon ion beam extracted through theextraction aperture.
 3. The ion source of claim 1, further comprising acontroller to independently control an output of the first bias powersupply and the second bias power supply.
 4. The ion source of claim 3,wherein the controller controls the output of the first bias powersupply and the second bias power supply to vary a uniformity of theribbon ion beam passing through the extraction aperture.
 5. The ionsource of claim 1, further comprising a first arc power supply to biasthe first cathode relative to the chamber walls and a second arc powersupply, different from the first arc power supply, to bias the secondcathode relative to the chamber walls.
 6. The ion source of claim 5,wherein an output of the first arc power supply is different from anoutput of the second arc power supply so as to change a uniformity ofthe ribbon ion beam extracted through the extraction aperture.
 7. Theion source of claim 5, further comprising a controller to independentlycontrol an output of the first arc power supply and the second arc powersupply, wherein the controller independently controls the output of thefirst arc power supply and the second arc power supply.
 8. The ionsource of claim 7, wherein the controller controls the output of thefirst arc power supply and the second arc power supply to vary auniformity of an ion beam passing through the extraction aperture. 9.The ion source of claim 1, further comprising a controller toindependently control an output of the first filament power supply andthe second filament power supply, wherein the controller independentlycontrols the output of the first filament power supply and the secondfilament power supply.
 10. The ion source of claim 9, wherein thecontroller controls the output of the first filament power supply andthe second filament power supply to vary a uniformity of an ion beampassing through the extraction aperture.
 11. An ion implanter,comprising: the ion source of claim 1; a beam profiler for measuring abeam current of the ribbon ion beam as a function of beam position; anda controller in communication with the ion source and the beam profiler,such that the controller controls an output of the first bias powersupply and the second bias power supply or controls the output of thefirst filament power supply and the second filament power supply so asto vary a uniformity of beam current of the ribbon ion beam.
 12. The ionimplanter of claim 11, further comprising a corrector magnet, whereinthe controller controls the corrector magnet to improve the uniformityof beam current of the ribbon ion beam after adjusting the output of thefirst bias power supply and the second bias power supply.
 13. The ionimplanter of claim 11, wherein the controller determines the uniformityof beam current of the ribbon ion beam based on input from the beamprofiler and adjusts the output of the first bias power supply and thesecond bias power supply so as to improve the uniformity of beam currentof the ribbon ion beam.
 14. The ion implanter of claim 11, wherein thecontroller determines the uniformity of beam current of the ribbon ionbeam based on input from the beam profiler and adjusts the output of thefirst filament power supply and the second filament power supply so asto improve the uniformity of beam current of the ribbon ion beam.
 15. Amethod of adjusting a uniformity of a ribbon ion beam extracted from adual cathode ion source, comprising: measuring a current of the ribbonion beam across its length at a plane of a workpiece; and adjusting aparameter of the dual cathode ion source to adjust the uniformity of theribbon ion beam in response to a measured current, wherein the parameterof the dual cathode ion source is selected from the group consisting ofa current flowing through a first filament, a current flowing through asecond filament, a voltage between the first filament and a firstcathode; a voltage between the second filament and a second cathode; avoltage between the first cathode and a wall of the dual cathode ionsource and a voltage between the second cathode and the wall of the dualcathode ion source.
 16. The method of claim 15, wherein the uniformityis adjusted by making the voltage between the first filament and thefirst cathode different from the voltage between the second filament andthe second cathode.
 17. The method of claim 15, wherein the uniformityis adjusted by making the voltage between the first cathode and the wallof the dual cathode ion source different from the voltage between thesecond cathode and the wall of the dual cathode ion source.
 18. Themethod of claim 15, wherein the uniformity is adjusted by making thecurrent flowing through the first filament different from the currentflowing through the second filament.